almost every time I show the two card monte the spectator will turn their hand over before the appropiate time what should I do

Okay well first off make sure you doing it to somebody that you can trust, a good way to see if you trust some random person is, do a few tricks for them first and if they are doing what you are telling them to do and nothing else, then you can do the 2 card monte to them, so make sure you can trust the spec. and make sure you make everything clear to them as you speak.

Have them set the card down on a table and place their fist on top. That way, it becomes very difficult for them to turn it over. That would be a quick fix. You are probably not mannaging yourself very well, and you should script out the routine, and read through and find any weak points that would allow the spectator to take controll.

It's your show, a spectator shouldn't be doing anything you don't want them to. Learn to control your audience, pick better spectators to hold the card. In Michael Close's Big Surprise he say's "There's an art to the building of suspense...." That line alone stops the spectator from jumping ahead. Alot of this stuff is trial and error, it doesn't come easy but you'll find something that works for you. good luck